1. Field of the Invention
The invention relates to an apparatus for achieving a controlled rate of discharge of a flowable particulate material from a bulk storage bag.
2. Description of the Related Art
Many manufacturing processes, such as processes performed in the chemical, pharmaceutical and food industries, utilize particulate materials. The particulates may take the form of pellets, flakes, powders or fibers. The particulates often are purchased from an outside vendor or supplier and are transported to a site where the particulates will be processed. In other situations, the particulates will be subjected to an initial processing at one manufacturing location of a company and then shipped to another facility of the same company for further processing.
Particulates traditionally were transported in rigid shipping containers, such as heavy metal tote bins or in Gaylord box containers. The heavy metal tote bins are emptied and then returned to the source of the particulate materials for reuse. The tote bins are heavy even in their emptied condition and occupy the same volume in their emptied condition. Hence, the return of the empty tote bin to the source of the particulates imposes a significant cost penalty and inconvenience. Gaylord box containers are disposable. However, waste disposal also creates inconveniences and imposes actual and environmental costs. Gaylord box containers are not constructed to function as in-plant use bins from which particulates may be dispensed. Thus, the contents of a Gaylord box must be transferred to another bin, thereby creating more handling and additional cost.
Bulk bags have been used in recent years for shipping, storing and dispensing particulate materials. Bulk bags are formed from a strong flexible material and offer several advantages. For example, bulk bags can be collapsed prior to filling, and hence do not occupy extensive space at the source of the particulate material. Similarly, bulk bags can be collapsed after emptying. Bulk bags that are intended for reuse can be shipped back to the source of the particulate material in a collapsed condition, thereby achieving space efficiencies. The characteristics of some particulate materials preclude reuse of the bulk bag. However, these one-way bulk bags still offer efficiencies in that the empty bulk bag can be collapsed easily into a size and shape for convenient disposal or recycling.
The typical bulk bag has a generally rectangular footprint to achieve optimum space utilization for storage and transportation. Bulk bags are available in several different sizes. One common bulk bag is approximately six feet tall when filled and approximately four feet square. The top of a typical bulk bag includes a plurality of looped straps so that the bulk bag can be lifted and suspended by the straps. The bottom of a bulk bag that is intended for reuse typically includes a spout that can be opened to discharge the particulate material from the bulk bag.
Bulk bags often are moved from one location to another in a manufacturing facility with a fork lift. The blades of a fork lift truck can be inserted through the looped handles of the bulk bag. The bag then is lifted and moved to a bag unloader. Other manufacturing facilities may utilize systems of hoists and trolleys to transport bulk bags.
The typical bulk bag unloader includes a frame and a device for suspending the bulk bag. The bottom end of the suspended bulk bag can be open so that the particulate material therein can be red from the bulk bag for use in a manufacturing process.
Particulates present unique product delivery problems that have been considered in industry for many years. More specifically, particulates may interfere with one another and prevent a pure gravitational flow comparable to the gravitational flow of liquids. The prior art includes particulate feeders that rely upon vibration to achieve a continuous flow of the particulates. The vibration causes the particles to move relative to one another. This movement prevents or minimizes interference between adjacent particles, and thereby permits a continuous flow of the particulates.
Bulk bag unloaders have addressed the product delivery problems of particulates in several different ways. For example, some manufacturers of bulk bag unloaders provide one or more paddles adjacent the suspended bulk bag. The paddles repeatedly strike the side of the bulk bag to generate sufficient movement so that the particulates can be dispensed continuously from the bulk bag. Vibra Screw, Inc. manufacturers a bulk bag unloader with an upwardly open support cone or hopper suspended from the unloader frame at a location beneath the bulk bag. A gyrator is mounted to the hopper and causes the suspended hopper to vibrate relative to the support frame. The vibration transmitted to the hopper acts on the bag spout to achieve a continuous flow of particulate material from the suspended bag.
Most manufacturing processes require the particulate materials to be delivered in controlled amounts or at controlled rates. However, the prior art bag unloaders are not at all well suited for controlling the rate of discharge of particulate materials from the bag. Bag unloaders can be used with load cells to measure the amount of particulate material that has been discharged from the bulk bag. For example, the load cells may be mounted beneath the legs of the frame from which the bulk bag is suspended. The paddles or the gyrator can be turned off when the load cells determine that a sufficient volume of the particulate materials has been discharged from the bulk bag. However, the particulate material will continue to flow gravitationally from the outlet spout of the bulk bag for a considerable time after the paddles or gyrator have been stopped. As a result, some other control means has been incorporated into the bag unloader.
Some bag unloaders have been adapted or retrofitted to include a gate valve or butterfly valve that can positively open and close the outlet from the bag unloader. Other bag unloaders have been adapted or retrofitted to include a structurally or functionally independent volumetric or gravimetric feeder. For example, a screw feeder can be disposed in proximity to the outlet from the bag unloader. Particulates are fed into the screw feeder and then are transported substantially horizontally away from the bag unloader and to a position where the particulate materials are dispensed from the screw feeder. Other bag unloaders have been used in conjunction with conveyors or vibratory feeders. A vibratory feeder generally defines an elongate tube or channel that is operative to vibrate along the axis of the tube or channel. This vibration causes the particulate materials in the tube or channel to incrementally shift along the length of the tube or channel.
Screw feeders, vibratory feeders or conveyors all permit relatively accurate feed rates. Additionally, the feeding of the particulates can be stopped merely by stopping the screw feeder, vibratory feeder or conveyor. However, the need for a structurally and functional independent feed apparatus to be used with the bulk bag unloader adds considerably to the size and cost of the unloader. For example, a volumetric feeder is likely to add 30%-40% to the price of the bulk bag unloader and is likely to increase the height of the bulk bag unloader by 3 ft.-5 ft. A valve is smaller and less expensive than a volumetric feeder. However, valves that are suitable for particulate material generally can function only in on/off modes, and do not permit flow regulation.
Accordingly, an object of the invention is to provide a bulk bag unloader that can achieve a variable flow rate without extensively increasing the cost or size of the unloader.